The document discusses material selection considerations for aircraft compressor blades. Key constraints include minimizing mass while withstanding high stresses, having high fracture toughness to tolerate impacts, and operating at temperatures up to 200°C. Titanium alloys currently provide the best balance of properties like strength and toughness relative to density, though carbon fiber reinforced polymers (CFRP) offer lower weight and are being developed. The selection process involves evaluating properties like strength and toughness relative to density for different materials to minimize weight while meeting requirements.

1. MATERIAL SELECTION FOR
AIRCRAFT COMPRESSOR
BLADE
Ahmad Bamasq
Ahmad Al Dakhil

2. Outline
• Introduction
• Constrains
• Selection Procedure
• Decision
• Future approach
• References

3. Introduction
• The majority of the thrust for propulsion in a modern
commercial jet engine comes from a large diameter fan at
the front of the engine, which is driven by the low-
pressure turbine at the rear of the engine. The fan, similar
to a room fan, consists of multiple blades that rotate about
the fan axis at high speed, and push the air backward
past the engine.

4. Constrains: Mass & Shape
• It is desired to minimize the weight of the fan blade to
decrease engine weight and then the takeoff weight. The
mass of the blades rotating at high speed creates high
stresses in the blades. It also requires the fan disk should
be strong enough to hold the blades.
• The blade has a specified size and shape.

5. Constrains: Strength
• The blade is to withstand rotational stresses equivalent to
70,000 psi (483 Mpa) in a material with density of titanium
(4500 kg/m3).
• We can find relation of σ/ρ > 107333 Pa / (kg/m3)

6. Constrains: Fracture Toughness
• Tolerance to damage (dents, cracks) from impact of
foreign objects (rocks, birds) is also important. A .02”
(0.51 mm) deep impact-induced crack should not
propagate under the cyclic loads imposed by centrifugal
force.
• Fast fracture will occur if the fracture toughness
• (Kc) > σ (πa)1/2
• (Kc) > ρ107333 (π 0.00051)1/2
• (Kc) / ρ > 4300 Pa (m)1/2 / (kg/m3)

7. Constrains: Cost & Temperature
• Cost is always a constraint in jet engines, particularly
commercial ones, and it is desired (though not essential)
to keep blade cost below $2000.
• The maximum service temperature is 200 C

8. Design Requirements
Function Aircraft compressor blades.
Constraints Size and shape are specified .
Strength: must not fail under design stresses.
High fracture toughness.
Maximum service temperature is 200 C
Objective Minimize mass
Free variables Choice of material

9. Indexes
• σ/ρ > 107333 Pa / (kg/m3)
• (Kc) / ρ > 4300 Pa (m)1/2 / (kg/m3)

10. Low alloy steel Stainless steel
Titanium alloys
Nickel-based super
10000
W rought magnesium alloys
CFRP, epoxy matrix (isotrop
Fracture toughness / Density
1000
100
10
1000 10000 100000
Tensile strength / Density

11. Low alloy steel Stainless steel
Titanium alloys
Nickel-based super
10000
W rought magnesium alloys
CFRP, epoxy matrix (isotrop
Fracture toughness / Density
1000
100
10
1000 10000 100000
Tensile strength / Density

12. 25000 Low alloy steel
Stainless steel
Titanium alloys
20000 Age-hardening wrought Al-alloys
Nickel-based superalloys
15000
Fracture toughness / Density
CFRP, epoxy matrix (isotropic
10000
W rought magnesium alloys
5000
200000 300000 400000 500000 600000 700000
Tensile strength / Density

13. Materials for blades
It is much lighter than normal (metallic) blade and
CFRB very strong but it’s expensive.
Titanium Titanium has very good balance between weight,
alloys drag and durability against vibrations, damage -
such as bird strikes - and erosion through sand, and
rain. However, it’s expensive.
Steel & Both have much bigger density
Nickel
alloys
Al & Mg Lighter and cheaper than Ti but the safety is low.
alloys

14. Ti blade vs. composite blade
• Today, the largest engine producers are Roll Royce and General
Eclectic. RR use hollow Ti blades while GE uses a composite blade.
•
• The choice of blade construction depends on a number of
considerations, thus there is no clear ‘right or wrong’ answer. Each
blade has advantages and disadvantages.
Factor ‘Preferred’ material
Fatigue strength Composites
Impact strength Ti alloys
Cost Both about equally (high)
Weight Depends on fan diameter
Durability Both appear adequate

15. • All RR aircraft engines use hollow titanium fan blades including
the Trent 1000 engine which is used in Boeing 787 Dreamliner.
• RR claims that CFRP blade is not aerodynamically efficient as Ti
blade. It has to be thicker to have the strength to deal with actual
requirements. In addition, Ti blades are more economical.

16. • However, Rolls-Royce is planning to
replace the Ti blades by CFRB blades.
• Rolls-Royce and GKN have developed
a CFRP blade that is as thin as the
titanium blades with manufacturing
costs.
• This fan blade has already undergone
ground tests, including blade-off and
bird strike tests.
• It is to begin flight tests on a Trent 1000
in the 2013 in Boeing 787.
• It could become available on a new
engine in the end of the decade
(beyond the Trent XWB).

17. • Since 1995, GE uses a CFRB fan blades for their
engines.
• Starting from GE90 for Boeing 777 and now: GEnx for
Boeing 787 Dreamliner which has both a front fan case
and fan blades made of carbon fiber composites.

18. • The CFRP with has titanium leading
edge for extra protection were a
lightweight and durable solution.
• Each fan blade weighs between 15
and 22 Kg. Every engine contains 22
of these fan blades, which add
approximately 900 kg to the engine's
thrust capability, providing better fuel
burn.

19. References
• http://www.me.jhu.edu/hemker/MatSel/Labs/Lab%202%2
0Fan%20Blade.doc
• http://www.sciencedirect.com/science/article/pii/S0921509
398011794
• http://www.flightglobal.com/news/articles/rolls-royce-
comes-full-circle-362251/
• http://www.geaviation.com/aboutgeae/presscenter/ge90/g
e90_20041116.html
• http://www.compositesworld.com/articles/aviation-outlook-
composites-in-commercial-aircraft-jet-engines

20. Thanks ..!